Hitherto, at the production of a flexible polyurethane foam having a density of 25 kg/m3 or less, in the case that water alone is used as a blowing agent, exothermic temperature at foaming and curing reaches 170° C. or higher because the amount of water to be added increases. Therefore, there is a possibility of autoignition owing to oxidative degradation (scorch) of polyurethane and also coloration of the resulting flexible polyurethane foam occurs by scorch. In order to avoid such situations, it is known to add methylene chloride or liquid carbon dioxide as a blowing aid without changing the conventional amount of water to be added.
However, methylene chloride is one of substances exerting a bad influence on the environment and the like and hence its use is regulated. On the other hand, foaming with liquid carbon dioxide necessitates a specialized apparatus for feeding liquid carbon dioxide under high pressure and, for smooth foaming, production conditions are limited and also a production cost increases. Thus, for the purpose of absorbing heat, there is known a technology of adding a polyolefin powder such as polyethylene powder (for example, cf. JP-T-2002-532596 (page 2) and JP-A-6-199973 (pages 2 and 3)).
In the above conventional technology of adding a polyolefin powder, though an effect on the decrease of the exothermic temperature at foaming and curing is observed, it is necessary to increase the amount of the polyolefin powder in order to lower a calorific value effectively. In that case, the increased amount of the polyolefin powder results in too high density of the resulting flexible polyurethane foam and also deterioration in physical properties such as compressive residual strain. Since the polyolefin powder cannot be blended in a sufficient amount in order to prevent the deterioration of such physical properties, there is a problem that the exothermic temperature cannot be effectively lowered at foaming and curing and, as a result, coloration by scorch cannot be reduced.